Ammonia is a commonly used chemical and is present in many different environments. For example, ammonia is present at various manufacturing sites for use in a wide range of chemical reactions, on farms where anhydrous ammonia is used as a fertilizer or where animal excrement is present but ventilation may be inadequate, or in offices and homes from the use of ammonia-containing cleansers.
Ammonia vapors can pose a significant health risk. For example, in the United States, OSHA has set an eight hour exposure limit of 25 parts per million for ammonia vapor and NIOSH recently lowered the IDLH (immediately dangerous to life and health) level from 500 parts per million to 300 parts per million. That is, exposure to ammonia vapor at concentrations greater than 300 parts per million for 30 minutes can result in death or irreversible damage to health.
Because of both the prevalence and potential health risks of ammonia, various respiratory products have been developed to reduce exposure to this compound and to other volatile nitrogen-containing compounds such as amines. These respiratory products typically contain a sorbent that can capture ammonia or volatile amines and thereby remove them from the air. Activated carbons are the most commonly used sorbent. Activated carbons are microporous and are good sorbents for a variety of compounds such as volatile organic compounds (VOCs) through the mechanism of physisorption. Physisorbed compounds are adsorbed but do not chemically react with the surface of the activated carbons.
Unlike many volatile organic compounds, ammonia and volatile amines typically are not effectively captured by physisorption. Rather, ammonia and volatile amines are usually more effectively captured through chemisorption where the compounds chemically react with the sorbent itself or with a compound impregnated into the sorbent. Many efforts have been made to impregnate activated carbons with various materials that can react with ammonia and volatile amines. For example, activated carbon has been impregnated with various mineral acids such as sulfuric acid and phosphoric acid. The highly corrosive nature of these impregnated mineral acids make the manufacture of these sorbents difficult. These acidic impregnates are often replaced with metal salts such as metal chlorides or metal acetates. The capacities of activated carbons impregnated with the metal salt can be comparable to activated carbons impregnated with mineral acid.
Siliceous materials have been treated with divalent metals and have been used, for example, in desulfurization (see Song et al. article in Advanced Materials Research, Vols. 926-930, 4322-4225 (2014)), to recover ammonia from industrial wastewater (see Yang et al. article in Membranes, 4, 40-54 (2014)), and combined with zeolite materials to trap and remove undesirable gases such as ammonia, ethylene oxide, formaldehyde, and nitrous oxide (see U.S. Pat. No. 7,559,981 B2 (Friday et al.)).